1. Field of the Invention
The present invention relates to a titanium target for sputtering and its method of making the titanium target, which is used for forming thin films as working materials or the like in manufacturing semiconductor elements such as LSI, ULSI and so on.
2. The Related Art
In order to solve signal delay because of a narrower line operation of electrode wiring, electrode materials to be used in LSI and ULSI are moving to high purity-high melting point metallic materials of the lower resistance, by increase in quick integration degree of the LSI of recent years, instead of polysilicon conventionally often used. There is molybdenum, tungsten, titanium or their silicides as the high purity-high melting point material to be used in the LSI and the ULSI. Titanium is especially desired in terms of superior specific strength, working property and corrosion proof property.
Sputtering is normally used when an electrode for semiconductor is formed with titanium. A titanium target of high purity to be used in the sputtering is normally manufactured as follows.
A high purity titanium material refined by an iodide thermal cracking method, an electrolysis method or the like is dissolved by a vacuum melting method of EB (electron beam) resolution or the like to make a plate shaped target through processes of casting, forging, rolling, heat treatment or the like. The above described dissolving method is put into practical use although a separating method for manufacturing the titanium target directly by the iodide thermal cracking method is researched.
In the sputtering using such a titanium target, unequal sputtering film thickness is said to be caused form different sputter efficiency through the crystal bearing of the crystal grains of the target. Therefore, the crystal bearing is generally averaged by the refining of the crystal grains of the titanium target. This is because the rolling and heat treatment are effected in the dissolving method.
But it has become extremely difficult to make films by the sputtering into a groove called contact hole because of extreme narrowing in the wiring width accompanied by recent further high integration, because there was no directional property in the sputter grains from the target as shown in FIG. 1 (A) in the titanium target where the crystal bearing is averaged.
As one of the measures, there is a method of arranging collimates between a basic plate and a target as shown in FIG. 1 (B). But in this method, there is a problem in that the sputtering efficiency is considerably lowered, because the sputter grains from the target are adhered on the collimates and the sputter grains to reach to the basic plate are considerably reduced in number. What is considered recently is an art of arranging the direction of the sputter grains from the target as shown in FIG. 1 (C). Japanese Laid-Open Patent Application Tokkaihei No. 5-214521 discloses a titanium target of the crystal structure where a priority bearing is considered around the (0002) parallel to the close-packed filling face from a point of view that the sputter grains are likely to be scattered in the close-packed filling direction of the crystal.
FIG. 2 shows the crystal structure at the room temperature of the titanium. There are (0002) as a face parallel to the close-packed filling face, (10 -10), (11 -20) or the like as a face vertical the close-packed filling face. The titanium target shown in Japanese Laid-Open Patent Application Tokkaihei No. 5-214521 has a similar orientation property, because titanium target manufactured by the general dissolving method is worked at comparatively low temperatures although the crystal is considered to be strongly orientated on the (0002).
In the sputtering into the groove called contact hole, the film making efficiency is made lower than without receiving of the rolling according to the researches by the present inventors although the soluble target where conventionally general crystal grain diameter has been refined is arranged in a sputter grains flying direction as compared with the crystal grain diameter controlled. This is because the scattering direction of the sputter grains is not controlled in a direction vertical to the target surface.
Namely, in the sputtering into the groove called contact hole, a direction of scattering sputter grains in the target is demanded to be controlled in a direction vertical to the target surface, because a direction of the sputter grains vertically with respect to a substrate to be formed in film is required to be controlled. But in the soluble target where conventionally general rolling is received, the sputter grains reaching to the bottom face of the contact hole is considerably reduced in number, because a jumping out direction of sputter grains is controlled in a direction different from the required direction without being controlled in a required direction.
An object of the present invention is to provide a titanium target for sputtering and its method of manufacturing the titanium target where the direction of the sputter grains to fly out from the target surface is controlled in a direction vertical with respect to the target surface.